The influence of short-range electrostatic forces on the measured local contact potentialdifference (CPD) by means of amplitude-modulation and frequency-modulation Kelvinprobe force microscopy (AM- and FM-KPFM) is discussed on the base of numerical andanalytical descriptions of both methods. The goal of this work is to help in interpretingrecent experimental results reporting atomically resolved CPD images, in particular onbulk insulating samples. The discussion is carried out on the basis of spectroscopic curves.The expression of the bias-dependent electrostatic force is derived from a previous workand is estimated between a tip with simple geometry and the (001) facet of a perfectalkali halide single crystal. The force, with a short-range character, scales as asecond-order polynomial function of the bias voltage. It is stated that the linear term isresponsible for the occurrence of the atomic-scale CPD contrast, while the quadraticone, involving the sample polarization, accounts for the detected signal by theKPFM methods. Nevertheless, analytical and numerical approaches stress theinfluence of the linear term on the measured CPD which intrinsically hindersthe possibility to perform quantitative CPD measurements, but also makes themeasured ‘pseudo-CPD’ strongly deviating from the surface potential. Hence, in theshort-range regime, AM- or FM-KPFM measurements neither reflect the CPD nor thelocal surface potential, but rather an effective value which is convoluted by thegeometric parameters of the tip, the so-called local CPD. It is also stated that thelocal CPD measured by means of AM- or FM-KPFM differs when sub-nanometervibration amplitudes of the cantilever are used. Otherwise, AM- and FM-KPFMmeasurements should be almost similar. At last, the influence of long-range, capacitive,electrostatic forces is discussed in conjunction with the short-range ones. Thisallows us to draw conclusions regarding the distance dependence of the localCPD which then exhibits a resonant behavior as a function of the tip–surfaceseparation. This phenomenon is expected to play a role in the KPFM imaging process.